A metallic item used as a core which reacts to the magnetic flux produced by a surrounding electrical coil(s). It travels on a longitudinal plane with reciprocating motion to perform a mechanical function. It may have facilities for attaching mechanical and/or electrical items such as linkage and/or contacts. It is a maintenance part for such items as RELAY, SOLENOID; RELAY-SOLENOID, ENGINE STARTER, ELECTRICAL; and SOLENOID, ELECTRICAL.